Chapter 9 - Thermochemistry Flashcards
Joule
Nm
N: newton
m: meter
kg*m^2/s^2
s: second
Newton
kg*m/s^2
Equation for q (energy required to raise/lower temp)
q = mCsp∆T
m: mass
Csp: specific heat
∆T: change in temp (final-initial)
First Law of Thermodynamics
The energy of the universe is constant
∆E = q + w
or
∆U = q + w
∆E/∆U: change in internal energy of the system
q: energy exchanged between the system and surroundings as heat
w: energy exchanged between the system and surroundings as work
Sometimes ∆U is used instead of ∆E (same meaning)
Temperature
A property which reflects the average energy in a particular system
Heat
The transfer of energy between two objects due to a temperature difference
Work
Force acting over a distance
w = -P∆V or -∆nRT
w: work
P: external pressure that causes compression or resists expansion
∆V: change in volume
∆n: gaseous products-gaseous reactants
R: 8.3145 J/mol*K
T: temperature (K)
-P∆V units is L atm, so convert to J
-∆nRT units is J
Work is negative when the system does work on the surroundings, but positive when the surroundings do work on the system.
State function
A property of a system which depends only on its present state
What is the sign of work when a system is doing work on its surroundings?
Negative
Found in Chapter 9: Chemical Energy
What is the sign of work when the surroundings are doing work on a system?
Positive
Change in enthalpy
∆H = ∆U + P∆V
or
∆H = ∆U + ∆nRT
H: enthalpy
U/E: internal energy of the system
P: pressure of the system
V: volume of the system
R: 8.3145 J/mol*K
Enthalpy is a state function
Hess’s Law
When going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether or not the reaction takes place in one step or a series of steps
1 L atm equals…
101.325 joules
Name some state functions
Temperature, pressure, volume, mass, enthalpy (H), internal energy (U)
Path-dependent functions
Heat (q) and work (w)
